Theα-decay of isobaric analogue states (which are forbidden by isospin selection rules) excited in24Mg and28Si through preton capture by23Na atEp=677 and 739 keV and by27Al atEp=295, 327 and 405 keV, respectively, have been studied using solid state track detectors. The ratio ofα-decay widths of the two resonance states in24Mg to the state at 1.632 MeV (2+) in20Ne yields the value 0.065 for the mixing parameterε and the value 4.01 keV for the Coulomb matrix element responsible for the isospin mixing in24Mg.
In28Si the measurement of theα-decay widths of the three resonance states resulted in the determination of the proton, gamma and alpha partial widths which comprise the total width of the resonance states. Limits have been set for the value of the two mixing parameters involved in this case. Upper limits of 16 and 39 keV have been obtained for the Coulomb matrix elements responsible for the isospin mixing in28Si.